September 2, 2008

In Today's One Minute Astronomer...

The "False Comet" Cluster

This sparkling group of associated stars in a rich section of the Milky Way presents the uncanny appearance to the naked eye of a small comet. It's a beautiful sight this time of year.

The Basics

• The “False Comet” is a group of two star clusters next to a string of brighter stars in the tail of the constellation Scorpius. The collection spans some 2 degrees of sky and looks like a small comet with a curved tail pointing northward into the Milky Way.

• Easily visible with the naked eye, the “False Comet” has been known since antiquity, although comet hunter Charles Messier was too far north to include it in his famous catalog.

• The star cluster NGC 6231 forms the “head” of the comet; the large open cluster Trumpler 24 forms the tail. While cataloged as separate clusters, these stars are physically associated and formed out of the same massive nebula only 6-8 million years ago. The collection is roughly 6,000 light years from Earth.

A Deeper Look

• If the head of the False Comet, NGC 6231, were as close as the Pleiades, it would appear about the same size. But the stars would be 50x brighter, some as bright as Sirius!

• In a 4-to-6-inch telescope, the False Comet looks like “tiny gems are dripping from an unseen hand and falling into a cache of overflowing jewels” according to Steven James O'Meara in his compendium of the Caldwell Objects.

Good To Know

This star collection only looks like a “False Comet” visually: looking at it through a telescope breaks the spell. But it's a wonderfully rich set of new stars set against the rich background of the Milky Way. If you're far enough south to see this collection, don't miss it.

Personal View

I saw the “False Comet” but once, without optics, from the high Andes in Northern Chile. Can't wait to see it through a small high-quality refractor. It's definitely on my top-ten list of things to see when I next head south.

--- Highly Recommended ---

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